The present invention relates in general to the management of a reactant in a fuel cell, and more particularly, to a flow field and method which optimizes reactant flow to electrodes in a fuel cell, such as a proton-exchange membrane fuel cell.
Fuel cell power plants are well known for converting chemical energy into usable electrical power, and have applications ranging from stationary power plants to automotive vehicles. Fuel cells typically include an electrolyte, which can be a liquid (e.g., phosphoric acid), a membrane (e.g., a proton exchange membrane) or a solid (e.g., a ceramic oxygen ion conductor), that is sandwiched between an anode electrode and a cathode electrode to form a cell assembly. The electrodes commonly contain a catalyst to promote the desired reactions. During operation, reactants are continuously supplied to the electrodes.
For example, in a proton-exchange membrane fuel cell the cell assembly is called a membrane-electrode assembly. On either side of the membrane electrode assembly are gas diffusion layers in contact with bipolar plates that comprise reactant flow fields for supplying a reactant fuel (e.g., hydrogen) to the anode, and a reactant oxidant (e.g., oxygen or air) to the cathode, the reactants diffusing through the gas diffusion layers to be evenly distributed on the anode or cathode catalyst layers. The hydrogen electrochemically reacts with the anode catalyst layer of the proton exchange membrane to produce positively charged hydrogen protons and negatively charged electrons. The electrolyte membrane only allows the hydrogen protons to transfer through to the cathode side of the membrane, forcing the electrons to follow an external path through a circuit to power a load before being conducted to the cathode catalyst layer. When the hydrogen protons and electrons eventually come together at the cathode catalyst layer, they combine with the oxidant to produce water and thermal energy. During operation of the fuel cell, the reactants (e.g., hydrogen, oxygen) are supplied to the electrode catalyst layers and the water produced at the cathode is removed from the fuel cell.